1. Field of the Invention
This invention relates to water-soluble acrylamide containing polymers and their use in, for example, flocculation of waste mineral processing streams.
2. Description of Background Information
In a number of mining industries such as copper, iron (taconite), potash, phosphate, coal, etc., waste products from the ore processing present serious disposal problems. For example, in the phosphate mining industry, processing leads to about one-third recoverable phosphate rock, about one-third sand tailings and about one-third fines of generally less than 150 mesh particle size. Aqueous suspensions of these ultrafine solids, which are associated with the ore, and which result from the processing, are referred to as "slimes." In the central area of the State of Florida, where a large portion of the U.S. phosphate mining industry exists, the problem of disposal of these slimes has become a major problem. The slimes may be contained in ponds or impounded areas surrounded by earthen dams and allowed to settle by gravity. However, this process takes a number of years. Alternatively, flocculants may be employed to concentrate the suspended solids.
Similarly, in the coal mining industry, large amounts of so-called "blackwater" are generated as a waste product of the coal cleaning plant operations. Such blackwater contains suspended coal fines and clays which desirably are removed prior to disposal or reuse of the water.
Mineral slimes exhibit colloid-like properties that are believed to be largely responsible for their poor dewatering characteristics and generally comprise very fine colloid-like particles (e.g., clays) suspended in water which, in the case of phosphate slimes, are largely Montmorillonite and Attapulgite clays. Attapulgite and Montmorillonite clays together are known to comprise approximately one-third of a typical phosphate slime. These clay materials are also well known for their colloid-like behavior when exposed to water. They tend to absorb water or to associate with water and form a suspended material which may be difficult to flocculate.
Water-soluble acrylamide polymers and copolymers are known as being useful for the flocculation of such phosphate slimes and blackwater suspensions. For example, commonly-assigned,, U.S. Pat. No. 4,529,782 (the disclosure of which is hereby expressly incorporated herein by reference), describes acrylamide-containing polymers, having an inrinsic viscosity of at least 15 dl/g, useful for flocculating phosphate slimes. The disclosed polymers may be terpolymers which may be represented by the following formula: ##STR2## wherein:
R, R.sub.1 and R.sub.3 are independently hydrogen or methyl;
R.sub.2.sup.+ is an alkali metal ion, such as Na.sup.+ or K.sup.+ ;
R.sub.4 is (1) OR.sub.5 where R.sub.5 is an alkyl group having up to 5 carbon atoms; (2) ##STR3## where R.sub.6 is an alkyl group having up to 8 carbon atoms; (3) ##STR4## where R.sub.7 is methyl, ethyl or butyl; (4) phenyl; (5) substituted phenyl; (6) CN; or (7) ##STR5##
a is from about 5 to about 90 mole percent;
b is from 5 to about 90 mole percent;
c is from about 0.2 to about 20 mole percent; and
d is an integer of from about 100,000 to about 500,000.
An example of such a terpolymer is one derived from a monomer mixture comprising about 54.3 mole percent acrylamide, about 4.6 mole % vinyl acetate and about 41.1 mole % sodium acrylate.
Also disclosed in said U.S. Pat. No. 4,529,782, are tetrapolymers obtained by the partial hydrolysis of the R.sub.4 group in the above formula.
A process for flocculating phosphate slimes employing such polymers is disclosed in commonly-assigned U.S. Pat. No. 4,452,940, the disclosure of which is hereby expressly incorporated herein by reference. The disclosed process generally comprises mixing a dilute aqueous solution of the polymer with the phosphate slimes under appropriate floc-forming conditions and allowing the suspended solids to settle from the slime to form an underflow of a more concentrated suspension of the clay solids and an essentially clear aqueous supernatant liquid.
Japanese Patent Publication No. 51-18913 describes a method of accelerating the aggregation/filtration of a fine mineral particle suspension using water-soluble terpolymers. These polymers are described as having a molecular weight above 1,000,000, preferably above 3,000,000, and comprise 5-50 weight % of a univalent salt of acrylic or methacrylic acid, 40-90 weight % of acrylamide, methacrylamide or methylol derivatives thereof, and 1-50 weight % of a weakly hydrophilic vinyl monomer. Table 1 therein describes a terpolymer prepared from 25 weight % sodium acrylate, 55 weight % acrylamide and 20 weight % vinyl acetate having a molecular weight of 1,500,000. German Offenlegungsschrift No. 2,543,135 discloses similar polymers as flocculants.
Copolymers of about 75 weight % acrylamide and about 25 weight % sodium acrylate are also known to be useful as flocculants in various aqueous systems. U.S. Pat. Nos. 3,790,476, 3,790,477, 3,479,282 and 3,479,284 disclose similar acrylamide-sodium acrylate copolymers and state that they are useful as flocculants.
U.S. Pat. No. 4,342,653 discloses a process for flocculating aqueous solid dispersions, such as phosphate slimes, with polymeric anionic flocculants comprising 40-99 mole % of repeating units derived from acrylamide, 1-35 mole % of repeating units derived from 2-acrylamido-2-methylpropane sulfonic acid (which is available from the Lubrizol Corporation under its tradename, and hereinafter referred to as, "AMPS") and 0-25 mole % of repeating units derived from acrylic acid.
U.S. Pat. No. 3,692,673 discloses water-soluble sulfonate polymers said to be useful as flocculants for aqueous systems, especially in combination with inorganic co-flocculants. The polymers contain units of the formula: ##STR6## wherein R.sup.1 is hydrogen or lower alkyl which may be substituted; R.sup.2 is a divalent or trivalent hydrocarbon or substituted hydrocarbon radical; M is a hydrogen atom or one equivalent of a cation; and x is 1 to 2. The polymers may be obtained by polymerizing,, either alone or in combination with other polymerizable vinyl monomers, a corresponding monomeric N-sulfohydrocarbon-substituted acrylamide (e.g. "AMPS" or its alkali metal or ammonium salt). It is further disclosed that the most useful polymers are homopolymers of such monomers and copolymers thereof with 5-95 weight % of an acrylic monomer such as acrylic or methacrylic acid or a salt or amide thereof (e.g., acrylamide). Specific disclosed copolymers are 80 weight % sodium "AMPS"/20 weight % sodium acrylate and 95 weight % sodium "AMPS"/5 weight % acrylamide.
U.S. Pat. No. 3,709,815 discloses copolymers of "AMPS" with acrylamide or acrylic acid as flocculants for aqueous systems. U.S. Pat. No. 3,709,816 discloses flocculating alluvial deposits (e.g., silt) in water systems with "AMPS" or sodium "AMPS" water-soluble polymers, which may be "AMPS" homopolymers or "AMPS" copolymers (containing at least 2 mole % "AMPS") with other comonomers, preferably acrylamide, acrylic acid, vinyl acetate, methyl acrylate or styrene. Other water-soluble monoethylenically unsaturated monomers which may be used include the alkali metal salts of acrylic and methacrylic acids, etc.
U.S. Pat. No. 3,975,496 discloses water-soluble copolymers useful as flocculants, especially in settling red mud obtained by the digestion of bauxite. The copolymers are, for example, acrylamide copolymers with either "AMPS" or sodium acrylate wherein the acrylamide is partially methylolated.
Conversely, U.S. Pat. Nos. 3,898,037 and 3,806,367 disclose acrylamide-sulfonic acid copolymers useful as dispersants or deflocculants for particles in aqueous systems. The copolymers (which have a molecular weight of 750 to 5,000,000) may comprise "AMPS" (or a salt thereof) copolymerized with a vinyl monomer, such as acrylic acid, esters thereof, acrylamide, vinyl acetate, etc.
Japanese Patent Publication No. 53-55488 discloses a flocculant comprising a water-soluble polymer containing about 90-99.8 mole % of an amide-type vinyl unit (e.g., acrylamide), about 0.1-5 mole % of a sulfonic group--containing vinyl unit (e.g., "AMPS" or its salt) and 0.1-5 mole % of a carboxyl group--containing vinyl unit (e.g., acrylic acid or its salt). The disclosed polymer is said to be useful for the sedimentation of used and waste water, for concentration, and for dehydration of various types of dirt.
Japanese Patent Publication No. 52-37580 discloses a method of aggregating solids suspended in aqueous media employing an aggregating agent which comprises a copolymer which exhibits a strong tendency to form threads and which is obtained by polymerizing a mixture of 65-98 weight % of acrylamide and 2-35 weight % "AMPS", where the total monomer concentration in the mixture is at least 15 weight %.
Japanese Patent Publication No. 54-61285 discloses a method for preparing a polymeric aggregating agent wherein the wet polymer is heated at a temperature above the copolymerization temperature and then dehydrated and dried. The polymer is a copolymer containing 55-98 weight % of acrylamide and 2-45 weight % "AMPS" (or its salt) and optionally, up to 20 weight % of a third copolymerizable monomer (e.g., sodium acrylate).
British Pat. No. 1,437,281 discloses high molecular weight, water-soluble acrylamide polymers useful as flocculating agents for, e.g., mineral processing slimes. The polymer comprises at least 50 weight % of acrylamide, 0-50 weight % of acrylic acid or its alkali metal salt and up to 5 weight % of other ethylenically unsaturated monomers such as "AMPS" or its alkali metal salts.
British Pat. No. 1,401,353 discloses the use of "AMPS"--containing polymers as retention and drainage aids in paper manufacturing. The polymer contains at least 2.5 mole % "AMPS" (or its salt) and 0-97.5 mole % of a comonomer such as acrylamide or sodium acrylate and, optionally, up to 20 mole % of other water-soluble comonomers and up to 10 mole % of water-soluble comonomers.
U.S. Pat. No. 4,024,040 discloses a radiation process for preparing water-soluble, high molecular weight acrylamide polymers useful as flocculating agents. The polymer is prepared from an acrylamide-type monomer, or mixtures thereof, which monomer may be acrylamide, an alkali metal acrylate, 2-acrylamido-2-methylpropane-sulfonic acid ("AMPS") or its salt, etc. No specific "AMPS"--containing polymers are disclosed.
West German Published (Non-Prosecuted) Application No. 1,442,408 discloses a flocculating agent comprising a copolymer of acrylamide and 1 to 10 % of compounds of the formula: ##STR7## wherein R.sub.1 is hydrogen or methyl, R.sub.2 is hydrogen or C.sub.1-4 alkyl, Y is SO.sub.3 X or O-13 SO.sub.3 X, X is a monovalent cation such an alkali metal, and n is a whole number such as 2 or 3.
It has now been found that improved flocculation efficiency is obtained in aqueous systems such as phosphate slimes and coal blackwater when the water-soluble acrylamide polymers of the present invention are used as flocculants.